Nadia is 51 years old and Ben is 9 years old. How many years will it take until Nadia is only 4 times as old as Ben?
Explanation: We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Nadia will be $51 + y$ years old and Ben will be $9 + y$ years old. At that time, Nadia will be 4 times as old as Ben. Writing this information as an equation, we get: $51 + y = 4 (9 + y)$ Simplifying the right side of this equation, we get: $51 + y = 36 + 4 y$ Solving for $y$ , we get: $3 y = 15$ $y = 5$.